BimlScript.com offers an introductory series on Getting Started with Biml and BimlScript. The first walkthrough in the series uses BIDS Helper to create a Biml file, and then uses Biml to generate a SSIS package in BIDS / SSDT.
The second article in the Getting Started with BimlScript series introduces BimlScript by incorporating BimlScript code nuggets in a Biml file. These code blocks make it possible to auto-generate multiple packages, while conditionally adding tasks to some packages but not others.
The third article in the Getting Started with BimlScript series familiarizes the reader with BimlScript directives, which are used to control how BimlScripts are processed. The walkthrough also shows how template tiers let a Biml author control the order in which BimlScript files are processed.